This invention relates in general to electro-chromatic devices and in particular to an electro-chromatic device that is capable of changing its response in both the visible and infrared light ranges.
There are multiple known technologies for making a “chameleon” cloth, or a coating structure, that can readily change color to allow for camouflage of personnel or objects from visible detection. Included in these known technologies are:
(1) Electro-chromatic dyes/pigments/polymers, where a material changes its electrooptic properties through the application of an electric potential across the material.
(2) Thermo-chromatic dyes/pigments, where a material changes color as its temperature changes. For example, a special dye may be used that contains liquid color crystals inside miniature capsules. When the temperature of a fabric treated with such a dye changes, the crystals can lose their color and become clear, revealing the color of a material that is underneath the dyed fabric.
(3) Electro-strictive polymers, or dielectric elastomers, where the material can reduce or increase its volume by 30%, when exposed to an electric field. This physical change may be linked to a color change of the material.
(4) Electrically conductive polymers where electrons can move from one end of the polymer to the other when the polymer is exposed to electic or chemical stimulations. This physical change may be linked to a color change of the material.
Referring now to FIG. 1, there is shown a cross sectional view of a typical electro-chromic device 10 that has multiple layers of material deposited between two glass substrates 12. Alternately, the multiple layers may be deposited upon a single glass substrate (not shown). As shown in FIG. 1, upper and lower transparent conductors, 14 and 16, respectively, are deposited the inner surface of each of the glass substrates 12. An electro-chromatic layer 18 is deposited upon the lower surface of the upper conductor 14 while an ion storage layer 20 is deposited upon the upper surface of the lower conduction 16. The electro-chromatic layer 18 is formed from a material that changes color upon receiving charged ions. Finally, a layer of polymer electrolyte 22 is positioned between the electro-chromatic layer 18 and the ion storage layer 20. The transparent conductors 14 and 16 are electrically connected through a switch 24 to a voltage supply 26. Upon closure of switch 24, a voltage is applied across the layers placed between the glass substrates 12 and drives ions from the ion storage layer 20 into the electro-chromatic layer 18 to cause a change of color of the device 10.
In many cases, instead of utilizing dual or single glass substrates, the transparent conductor material can be coated onto a polymer to make a semi-flexible device, where the limits on flexibility are determined by the point where the transparent conductor loses function. Recent examples have also been shown where a conducting polymer is used as the transparent conductor and as the electro-chromic-material, which results in simplified device construction.
However, there still remains a need for an improved cloth or coating structure, which can readily change color, to allow for the camouflage of personnel or objects from visible detection. Similarly, there remains a need for a cloth or coating structure which can control the Infra-Red (IR) signature of objects, to provide camouflage from passive IR sensors. Ideally, these two needs would be met with a single cloth or coating structure.